Perforated valve spray disk

ABSTRACT

A perforated spray disk, particularly suitable for use in injection valves of fuel injection systems of internal combustion engines. The spray disk has at least one conical spray opening which expands in the direction of flow.

This application is a continuation of application Ser. No. 08/202,416,filed Feb. 28, 1994, now abandoned.

FIELD OF THE INVENTION

The invention relates to a perforated spray disk for a valve, and to amethod for producing spray openings in a perforated spray disk.

BACKGROUND OF THE INVENTION

In German patent application P 42 21 185.9 it has already been proposedto generate, by punching or electrical discharge machining (EDM), sprayopenings in perforated spray disks. The spray openings possess anon-cylindrical shape after an additional process step involving partialdeep drawing of the perforated spray disk. In this known perforatedspray disk, the spray openings are first produced vertically andcylindrically in a flat piece of sheet metal by punching or electricaldischarge machining. In a subsequent process step a central region ofthe perforated spray disk, in which the spray openings are located, isplastically deformed by deep drawing, causing the central region of theperforated spray disk to take on a domed shape. The result of the deepdrawing is that the spray openings are stretched farther out downstreamthan upstream, so that truncated conical flares of the spray openingsare produced.

In addition to DE-OS 38 01 778 mentioned above, it is also already knownfrom U.S. Pat. No. 4,080,700 to use flaring spray holes in a sprayplate. The spray holes produced in the spray plate each have atriangular cross section; the triangles being approximately equilateral.After the spray holes are produced, the spray plate is domed with apunch, so that as a result the spray holes flare out in the direction ofmotion of the punch, since the spray holes are stretched farther outdownstream than upstream. Thus at least two mutually independentmanufacturing methods are needed to achieve this configuration of thespray holes. The flares of the spray holes cannot be completelysymmetrical over their entire length because of the doming of the sprayplate.

Since the central region of the perforated spray disk is domed, at leastone spray opening is inclined with respect to a lengthwise valve axis,and the truncated conical flare is not necessarily completelysymmetrical over the entire length of the spray opening. The sprayopenings are therefore produced in an unflared shape, and only expandeddownstream by an additional process.

Moreover, it is also known from DE-OS 38 01 778 to use for fuelinjection valves a diaphragm made of a material with great naturalhardness, for example monocrystalline silicon, whose fuel dischargeopenings are produced by etching. In order to produce contours for thefuel discharge openings which deviate from a cylindrical shape, anothercomplex and costly treatment with high-energy radiation, e.g. laserradiation, is used after the etching step.

SUMMARY AND ADVANTAGES OF THE INVENTION

The present invention provides a perforated spray disk for a valvehaving a lengthwise valve axis and a fluid flow direction comprising: aspray disk central region, the central region having at least one sprayopening; the at least one spray opening having a truncated conical formwhich expands in the flow direction around an opening axis; and theopening axis and the lengthwise valve axis being parallel.

An advantage of the spray disk is that because of the at least singlespray opening with positive conicality--i.e. with a wall that flaresdownstream in truncated conical form--extending parallel to thelengthwise valve axis, the medium separates from the wall of the sprayopening as it flows through, except at the flow inlet which acts as anaperture. The wall of the spray opening extends in a completelysymmetrical manner about one opening axis. A particular advantage ofthis configuration of the spray opening is the elimination of additionalprocessing methods, so that the shape of the spray opening originallycreated by electrical discharge machining can remain.

The spray openings with positive conicality produced parallel to thelengthwise valve axis have the advantage of preventing the flow fromskipping against the inner wall, so that variations in the volume ofmedium flowing through the spray openings can be minimized when largequantities of parts are manufactured.

The present invention for producing spray openings in a perforated spraydisk also provides a method for producing a perforated spray disk withat least one spray opening comprising the steps of: (a) removingparticles from the perforated spray disk by electrical dischargemachining perpendicular to a surface of the perforated spray disk; and(b) flushing the detached particles out with a dielectric so that aconical spray opening results.

An advantage of this method is that is allows for particularly simple,time-saving, and cost-effective production of the spray openings in theperforated spray disk which flare out in a truncated conical shape. Theat least single spray opening is produced with extreme accuracy,parallel to the lengthwise spray axis, with no need for furtherprocessing of the spray opening thereafter. Using a tool electrode thatpenetrates into the perforated spray disk against the later flowdirection of the medium (for example fuel), perforated spray diskmaterial is eroded away and flushed out with a dielectric, against themotion of the tool electrode, through a working gap. In the process, theconical shape of the spray opening, which has its greatest diameterwhere the tool electrode enters the perforated spray disk, is producedsimply because the spark path from the tool electrode to the wall of thespray opening is shortened by the detached particles flushed away alongwith the dielectric. In order to retain, after the tool electrode hasbroken through the perforated spray disk, the conicality that isproduced during electrical discharge machining and is desired in theinterest of. minimal variation in flow volume, it is particularlyadvantageous to use a dielectric to counterflush from the side of theperforated spray disk opposite to the insertion of the tool electrode.The dielectric, utilized under pressure, ensures that the detachedparticles emerge from the perforated spray disk only in the direction ofentry of the tool electrode, and reinforces flushing in the oppositedirection from the EDM process. The originally generated conicality ofthe spray opening is thus retained.

It is also advantageous that the central region is flat, which allowsthe fluid which passes through the spray openings to be directedstraight ahead.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is depicted in simplified formwith reference to the following drawings, and explained further in thedetailed description below:

FIG. 1 shows a partial depiction of a fuel injection valve with aperforated spray disk according to the invention.

FIG. 2 shows the perforated spray disk according to the invention.

FIG. 3 shows a spray opening according to the invention with positiveconicality.

FIGS. 3A and 3B show spray openings with negative conicality and acylindrical form, respectively.

FIG. 3C is a diagram of the variation in static flow volumes through thespray openings shown in FIGS. 3, 3A, and 3B as a function of conicality;and

FIG. 4 shows the production of a perforated spray disk according to theinvention.

DETAILED DESCRIPTION

FIG. 1 partly depicts, as an exemplary embodiment, a valve in the formof an injection valve for fuel injection systems of mixture-compressing,externally-ignited internal combustion engines. The injection valve hasa tubular valve seat support 1 in which a lengthwise opening 3 ispresent concentrically with a lengthwise valve axis 2. Arranged in thelengthwise opening 3 is a valve needle 5, for example tubular in shape,which is attached at its upstream end 6 to a valve closure element 7,for example spherical in shape, on whose periphery for example fiveflattened areas 8 are provided.

The injection valve is actuated in a known manner, for exampleelectromagnetically. An indicated electromagnetic circuit with a magnetcoil 10, an armature 11, and a core 12 is used to move valve needle 5axially and thus to open the injection valve against the spring force ofa return spring (not depicted) and to close it. Armature 11 is attachedto the end of valve needle 5 that faces away from valve closure element7 by, for example, a weld bead produced by a laser, and is aligned withcore 12. Magnet coil 10 surrounds core 12, which represents the end,enclosed by magnet coil 10, of an inlet tube (not shown in greaterdetail) used to deliver the medium (in this case fuel) being metered bythe valve.

A guide opening 15 of a valve seat element 16 guides valve closureelement 7 during its axial motion. The cylindrical valve seat element 16is mounted in a sealed manner, for example by welding, in lengthwiseopening 3 extending concentrically with lengthwise valve axis 2 into theend of valve seat support 1 which lies downstream and opposite core 12.The periphery of valve seat element 16 has a slightly smaller diameterthan lengthwise opening 3 of valve seat support 1. At its lower surface17 facing away from valve closure element 7, valve seat element 16 isconcentrically and permanently attached to a bottom part 20 of aperforated spray disk 21, which is for example cup-shaped, so that anupper surface 19 of bottom part 20 rests against lower surface 17 ofvalve seat element 16.

Valve seat element 16 and perforated spray disk 21 are attached, forexample, by a peripheral, sealed first weld bead 22 produced, forexample, with a laser. This type of assembly eliminates the risk ofundesired deformation of bottom part 20 in its central region 24, inwhich at least one, or for example four, spray openings 25 that areformed by EDM and have positive conicality, i.e. that flare downstreamin truncated conical fashion, are located.

Continuous with bottom part 20 of cup-shaped perforated spray disk 21 isa circumferential retaining rim 26 that extends axially away from valveseat element 16 and is bent outward conically toward its end 27.Retaining rim 26 has at its end 27 a greater diameter than the diameterof lengthwise opening 3 of valve seat support 1. Since the peripheraldiameter of valve seat element 16 is less than the diameter oflengthwise opening 3 of valve seat support 1, only a radial press fit ispresent between lengthwise opening 3 and retaining rim 26 of perforatedspray disk 21, which is bent slightly outward in conical fashion.Retaining rim 26 thereby exerts a radial spring action on the wall oflengthwise opening 3. This prevents chip formation on the valve seatpart and on lengthwise opening 3 when the valve seat part, consisting ofvalve seat element 16 and perforated spray disk 21, is inserted intolengthwise opening 3 of valve seat support 1.

The depth to which the valve seat part, consisting of valve seat element16 and cup-shaped perforated spray disk 21, is inserted into lengthwiseopening 3 determines the preset stroke length of valve needle 5, sincethe one end position of valve needle 5 when magnet coil 10 is notenergized is defined by contact between valve closure element 7 and avalve seating surface 29 of valve seat element 16.

The other end position of valve needle 5 when magnet coil 10 isenergized is defined, for example, by contact between armature 11 andcore 12. The distance between these two end positions of valve needle 5thus represents the stroke length.

Retaining rim 26 of perforated spray disk 21 is attached at its end 27to the wall of lengthwise opening 3, for example by means of aperipheral, sealed second weld bead 30. Second weld bead 30, like firstweld bead 22, is produced for example by means of a laser. Sealedwelding of valve seat element 16 to perforated spray disk 21, and ofperforated spray disk 21 to valve seat support 1, is needed so that themedium used cannot flow through between lengthwise opening 3 of valveseat support 1 and the periphery of valve seat element 16 to sprayopenings 25, or between lengthwise opening 3 of valve seat support 1 andretaining rim 26 of the cup-shaped perforated spray disk 21 directlyinto an intake duct of the internal combustion engine.

The spherical valve closure element 7 interacts with valve seatingsurfaces 29, which taper in truncated conical fashion in the flowdirection, of valve seat element 16, which extends axially between guideopening 15 and lower surface 17 of valve seat element 16. Valve seatelement 16 has a valve seat element opening 34, facing magnet coil 10,which has a greater diameter than the diameter of guide opening 15 ofvalve seat element 16. A segment 33 adjoining valve seat element opening34 in the direction of perforated spray disk 21 is characterized by itstruncated conical taper down to the diameter of guide opening 15. Valveseat element opening 34, with its adjacent truncated conical segment 33,serves as a flow inlet, so that the medium can flow from a valveinterior 35 delimited radially by lengthwise opening 3 of valve seatsupport 1 to guide opening 15 of valve seat element 16.

To ensure that the flow of medium also reaches spray openings 25 ofperforated spray disk 21, for example five flattened areas 8 areproduced on the periphery of spherical valve closure element 7. The fivecircular flattened areas 8 allow the medium to flow through, when theinjection valve is open, from valve interior 35 to spray openings 25 ofperforated spray disk 21 which flare out in truncated conical form. Forprecise guidance of valve closure element 7 and thus of valve needle 5during axial motion, the diameter of guide opening 15 is such that thespherical valve closure element 7 projects beyond its flattened areas 8through guide opening 15 with a slight radial spacing.

A protective cap 40 is arranged at the periphery of valve seat support 1at its downstream end facing away from magnet coil 10, and attached tovalve seat support 1 for example by means of a snap-on connection. Asealing ring 41 provides sealing between the periphery of the injectionvalve and a valve receptacle (not shown), for example the intake duct ofthe internal combustion engine.

FIG. 2 shows perforated spray disk 21 with its spray openings 25arranged in central region 24 which flare out downstream in a truncatedconical shape, i.e. have positive conicality facing in the flowdirection. The for example four spray openings 25 are located, forexample, symmetrically about lengthwise valve axis 2, distributed in theform of the corners of a square, and are thus each at the same distancefrom one another and from lengthwise valve axis 2. The spray disk has anupper surface 19 and lower surface 52.

FIG. 3 depicts an enlarged spray opening 25 with positive conicality inbottom part 20 of perforated spray disk 21. The dashed lines with arrowsillustrate the flow of the medium, for example a fuel, inside sprayopening 25. As fuel flows through spray opening 25, an annular region 45of flow separation, in which there is almost no contact between the flowof medium and wall 44 of spray opening 25, occurs as a result of theflow velocity and a wall 44 of spray opening 25 that flares out in atruncated conical shape. The outside diameter D of this almostmedium-free annular region 45 expands downstream along with the diameterof spray opening 25. The inside diameter d of annular region 45 remainslargely constant, since it is formed by the edge of the medium as itflows vertically downstream. Ideally, the annular flow separation region45 begins immediately downstream of a flow inlet 47 of spray opening 25.

Thus the spray openings 25 are configured so that an aperture effectwith flow constriction is achieved at flow inlet 47. Because sprayopening 25 flares out immediately downstream from flow inlet 47, theflowing medium lifts away from wall 44 of spray opening 25 after flowinlet 47, which acts as an aperture. Reattachment of the flow to wall 44of spray opening 25 after entering spray opening 25 is prevented, in anadvantageous manner, by the positive conicality, thus eliminating, forexample, fluctuations in static flow volume Q_(stat). The greatestdiameter of spray opening 25 at flow outlet 48 is, for example, 5 to 20micrometers greater than the diameter of spray opening 25 at flow inlet47, for a length l of approximately 200 micrometers for spray opening25. Configuring spray openings 25 in perforated spray disk 21 accordingto the invention with positive conicality ensures that flow skippingdoes not occur, i.e. that the flow cannot alternate between a state incontact with wall 44 and a state separated from wall 44, so that theflow volume per unit time remains constant. Spray openings 25 withpositive conicality consequently prevent flow skipping along wall 44 ofspray opening 25, and thus also prevent quantitative changes in staticflow volume Q_(stat), meaning most importantly that variations in flowvolume through spray openings 25 can be kept very low when large numbersof perforated spray disks are manufactured.

In contrast to this, FIG. 3A shows a spray opening 25A with negativeconicality in a perforated spray disk 21A, and FIG. 3B shows acylindrical spray opening 25B, with no conicality, in a perforated spraydisk 21B.

The flow of medium passing through spray opening 25A, which is againindicated by dashed lines and arrows, is in contact with a wall 44A ofspray opening 25A that is of truncated conical shape and tapersdownstream, but can separate if perforated spray disk 21A is evenminimally off-axis. The consequence of spray openings 25A with negativeconicality is that considerable fluctuations in flow volume can occurdue to differences in flowthrough time and alternation between attachedand separated flow. The problem of alternation between attached andseparated flow at a wall 44B can also occur in the cylindrical sprayopening 25B depicted in FIG. 3B, in which the attached and separatedflow is shown in simplified and exaggerated fashion. Electricaldischarge machining of spray openings 25B in precisely cylindrical form,with deviations in the nanometer range, is moreover extremelycost-intensive, so that each cylindrical spray opening 25B still hassome minimal positive and/or negative conicality; this explains thevariations in flow volume of the medium through spray openings 25B whenlarge numbers of perforated spray disks 21B are manufactured.

FIG. 3C shows a diagram of the variation in static flow volume Q_(stat)as a function of the conicality of spray openings 25, 25A, and 25B,which is plotted as the difference between outlet surface area A_(A) andinlet surface area A_(E). This clearly illustrates the much lowervariation in flow volume with spray openings 25 having positiveconicality, compared with cylindrical spray openings 25B and sprayopenings 25A having negative conicality.

Spray openings 25 with positive conicality are produced with anelectrical discharge machining method that is depicted in simplified andschematic form in FIG. 4, using a dielectric 50 such as, for example,water. Electrical discharge machining is a method in whichshort-duration, nonsteady-state, temporally distinct discharges takeplace between a tool electrode 51 and the workpiece, in this caseperforated spray disk 21, in order to remove material from theworkpiece. The fluid dielectric 50 is provided between tool electrode 51and perforated spray disk 21. This makes it possible to transfer thecontour of tool electrode 51, manufactured to a specific dimension andshape, into spray opening 25 of perforated spray disk 21. To guaranteedefined seating of perforated spray disk 21, and to ensure that toolelectrode 51 is inserted into perforated spray disk 21 preciselyperpendicular to a lower surface 52 of bottom part 20 of perforatedspray disk 21, perforated spray disk 21 is precisely mounted by means ofbearings 53 on, for example, a workpiece table 54.

Machining of perforated spray disk 21 to form spray openings 25 thustakes place from the downstream lower surface 52, i.e. the EDM processoccurs in a direction opposite to the later direction of fuel flow.Outlet surface A_(A) of spray opening 25 is produced at lower surface 52of perforated spray disk 21, which during the EDM process faces toolelectrode 51; and inlet surface A_(E) of spray opening 25 is produced atupper surface 19 of perforated spray disk 21. As tool electrode 51penetrates through perforated spray disk 21 from lower surface 52 toupper surface 19, flushing with dielectric 50 occurs withoutpressurization on the electrode side. In addition to flushing outdetached particles, dielectric 50 cools tool electrode 51 and providesinsulation. Flushing with dielectric 50 occurs from lower surface 52 ofperforated spray disk 21, until upper surface 19 of perforated spraydisk 21 is reached. Until tool electrode 51 has penetrated through thematerial of perforated spray disk 21, the detached particles must beconveyed to lower surface 52 and there flushed out.

Because of the time difference between electrical discharge machining atlower surface 52 of perforated spray disk 21 and electrical dischargemachining at upper surface 19 of perforated spray disk 21, and thedistance traveled by the detached particles emerging from working gap 56formed between tool electrode 51 and wall 44 of spray opening 25 as itis being created, unequal amounts of material are eroded away from wall44 over length l. Specifically, as they travel toward lower surface 52,the particles shorten the spark path from tool electrode 51 to wall 44,so that more material is removed at the entry point of tool electrode 51than at the instantaneous position of front end 58 of tool electrode 51.The EDM process in perforated spray disk 21 thus produces a conicalcontour of wall 44 until upper surface 19 is reached.

Immediately after tool electrode 51 breaks through at upper surface 19of perforated spray disk 21, the detached particles can emerge in thedirection of workpiece table 54, so that the resulting conicality ofwall 44 would be very quickly compensated for and the completed sprayopening 25 would take on a cylindrical shape. In order to retain theconicality produced during electrical discharge machining, which isdesired for the sake of minimizing flow volume variations, a dielectric50A, for example also water, is made ready for counterflushing, forexample through a passage in workpiece table 54. The direction ofcounterflushing with dielectric 50A is from workpiece table 54 intospray opening 25 of perforated spray disk 21. It is particularlyimportant that counterflushing with dielectric 50A be present even whilethe EDM process is taking place in perforated spray disk 21, so that assoon as tool electrode 51 breaks through the material of perforatedspray disk 21, counterflushing is already effective at upper surface 19.

To prevent dielectric 50 from emerging from perforated spray disk 21 atupper surface 19, dielectric 50A flows under a pressure p that isgreater than atmospheric pressure, in a direction opposite to theworking direction of tool electrode 51. Counterflushing with dielectric50A guarantees that all detached particles flow out via lower surface52, thus preventing any compensation for conicality. While thecounterflushing process with dielectric 50A is still occurring, toolelectrode 51 is moved out of perforated spray disk 21 toward lowersurface 52, away from workpiece table 54.

The degree of conicality, i.e. the angle between wall 44 and an openingaxis 60 of spray opening 25 running parallel to lengthwise valve axis 2,depends on a variety of parameters of the EDM process, such as the type,shape, and wear of tool electrode 51, the material of perforated spraydisk 21, the nature of dielectric 50, 50A, and the magnitudes of the EDMvoltage and discharge values. Another critical factor governing theconicality is the particular length/diameter ratio selected for sprayopening 25. The EDM parameters can be left unchanged as compared withthe production of, for example, cylindrical spray openings 25, sincecounterflushing with dielectric 50A has no influence of the usability oftool electrode 51. Conical spray openings 25 in perforated spray disks21 can therefore be produced easily and with very high quality byelectrical discharge machining proceeding from lower surface 52 againstthe later flow direction of the fuel, while simultaneouslycounterflushing with a dielectric 50A from upper surface 19 ofperforated spray disk 21.

While the present invention has been described in relation to theabove-described embodiment and method it is envisioned that otherembodiments and methods may fall within the scope of the presentinvention.

What is claimed is:
 1. A perforated spray disk for a valve having a lengthwise valve axis and a fluid flow direction, comprising:an upper surface; a lower surface; a metal spray disk central region, the central region having at least one spray opening; the at least one spray opening being formed by electrical discharge machining and having a frustoconical form which expands in the flow direction around an opening axis, the at least one spray opening frustoconically extending from the upper surface to the lower surface; and the opening axis and the lengthwise valve axis being parallel; wherein the at least one spray opening of the perforated spray disk includes a plurality of spray openings and the spray openings are configured with identical spacing from one another.
 2. The perforated spray disk as recited in claim 1 wherein there are four spray openings identically spaced from one another, the four spray openings forming a square shape, each of the four spray openings being positioned at a respective corner of the square shape. 